Color cathode ray tube electrode support arrangement



Dec. 15, 1970 SUSUMU og ETAL 3,548,234

COLOR CATHODE RAY TUBE ELECTRODE SUPPORT ARRANGEMENT Filed June 13, 2Sheets-Shem l SUSUMU YOSHIDA AKIO OHGOSHI SENRI MIYAOKA YOSHIHARUKATAGIRI ATTORNE Y United States Patent U.S. (Tl. 31382 3 ClaimsABSTRACT OF THE DISCLOSURE A color picture tube or other cathode raytube in which a plurality of electron beams eminating from one or morecathodes are made to converge substantially at the optical center of anelectrostatic focusing lens which focuses the beams on an electronreceiving screen. The grids forming the electron gun are supported by aninsulating mem her. The grid in which the electrostatic focusing lens isformed has a diameter greater than the other grids or electrodes inorder to permit the focusing lens to have as fiat opposing surfaces aspossible, that is, surfaces with a maximum radius. The outer diameter ofthe support member for the grids is essentially equal to the innerdiameter of the neck of the cathode ray tube. This is accomplished byforming the insulating support in two parts with the grid forming thefocusing lens extending between the two parts and being supported byeach of the insulating members.

This application is a continuation-in-part application of our copendingapplication filed I an. 12, 1968, entitled Cathode Ray Tube and whichbears US. Pat. No. 3,448,316.

This invention generally relates to cathode ray tubes and isparticularly directed to improvements in color cathode ray tubes of thetype in which a single electron gun is provided for emitting a pluralityof electron beams in order to produce a color picture such for exampleas in color television receivers.

Existing color picture tubes are usually of the multi-gun type andinclude three independent electron guns emitting respective electronbeams which are modulated by corresponding color signals and acted uponby a grid system so as to be focused on a collector or electronreceiving screen which may be simply a phosphor or luminescence screenor a phosphorus screen with a perforated electrode or shadow mask infront thereof. The three electron guns have to be aligned with respectto each other so that the emitted electron beams converge at theelectron receiving screen. Such color picture tubes of the multi-guntype are disadvantageous in that it is difficult to obtain and maintainthe precise alignment of the three electron guns required for theconvergence of their beams on the electron receiving screen and anymisconvergence of the beams causes deterioration of the quality andresolution of the color picture that results.

In an attempt to avoid the above-mentioned disadvantages and limitationsof the existing color picture tubes of the multi-gun type, it has beenproposed to provide a color picture tube of the single gun plural beamtype in which a single electron gun emits three beams from either threerespective cathodes or a single cathode and the three electron beams arepassed through a lens like focusing system so as to converge at theelectron receiving screen. However, in the tubes of the single gunplural beam type heretofore proposed, no more than one of the electronbeams passes through the lens like focusing system at the 3,548,234Patented Dec. 15, 1970 optical axis of the latter and the beams thatpass through the focusing system at a distance from the optical axis aresubject to coma and spherical aberration. By reason of such coma andspherical aberration and the consequent deterioration of the quality ofthe color picture that results, color picture tubes of the single gunplural beam type have not enjoyed any wide-spread use.

In my copending patent application filed J an. 12, 1968, and bearing US.Pat. No. 3,448,316 entitled Cathode Ray Tube, there is described acathode ray tube adapted for use in a color television receiver andwhich is provided with a single electron gun. This gun includes acathode structure that emits electrons which are formed into a pluralityof electron beams and such beams are made to converge substantially bythe optical center of a lens like electrostatic focusing lens which iscommon to all the beams and focuses the beams on the electron receivingscreen whereby the introduction of spherical aberrations is diminished.

In cases where the electron beams are emitted parallel to each other,the convergence of the beams at the optical center of the lens likefocusing means is effected by an auxiliary electrostatic lens locatedbetween the grid structure which forms the electron beams and thefocusing lens. When it is desired that the beams focused on the electronreceiving screen be converged at a common point on the screen the beamswhich diverge from the focusing lens are acted upon by eitherelectrostatic or magnetic deflection means located between the focusinglens and the screen.

In most prior art cathode ray tubes which utilize an electron gun havinga plurality of grids, the grids all generally have the same diameter.The electron gun is positioned in the neck of the cathode ray tube andthe various grids and electrodes are held in position spaced from eachother by an elongated insulating support. This insulating support ismade in one piece and is positioned between the grids and the interiorsurface of the neck of the cathode ray tube. In such prior art cathoderay tubes, the diameter of the respective grids forming the electron gunare limited to a diameter less than the interior diameter of theinsulating support member.

The disadvantage with such prior art type of electron guns is that thediameter of the individual grids limits the size of the electrostaticfocusing lens which can be formed. It is of course desirable that thisfocusing lens have as flat a surface as possible, that is, that thesurfaces of the electrostatic lens be formed with the maximum radius.The smaller the radius of the electrostatic focusing lens the greaterthe error that can be introduced due to various spherical aberrations.The radius of the electrostatic focusing lens, however, is limited bythe diameter of the grid within which it is formed.

In view of the foregoing, it is the primary object of this invention toprovide a cathode ray tube of the single gun plural beam type which isfree of the abovementioned disadvantages and which is particularlysuited to the formation of an electrostatic focusing lens having opposedsurfaces with a large radius.

Another object of this invention is to provide a cathode ray tube of thetype in which the electron gun has a plurality of grids and in which theinsulating support member for the grids is formed in at least twosections with the two sections being spaced from each other to permitinsertion therebetween of the grid within which the electron focusinglens is formed.

In accordance with this invention a cathode ray tube adapted for use asthe picture tube in a color television receiver is provided with anelectron gun which includes a cathode structure that emits electronswhich are formed by a grid structure into a plurality of electron beams.These beams are made to converge substantially at the optical center ofa lens like electrostatic focusing lens which is common to all of thebeams and focuses the beams on the electron receiving screen. Theinsulating support for the various grids is made in two sections and thetwo sections are spaced from each other to permit insertion therebetweenof the grid within which the electrostatic focusing lens is formed. Thisparticular grid accordingly has a diameter which can be substantiallyequal to the inner diameter of the neck of the cathode ray tube. In thismanner the electrostatic focusing lens can be formed with opposedsurfaces which have an exceptionally large radius to present arelatively flat surface and thereby diminish spherical aberrations.

The above and further objects, features and advantages of the presentinvention will appear from the following detailed description of apreferred embodiment of the invention which is to be read in conjunctionwith the accompanying drawings in which:

FIG. 1 is a diagrammatic view illustrating the optical equivalent of asingle gun plural beam system in which the beams are converged tosubstantially the optical center of an electrostatic focusing lens;

FIG. 2 is a schematic longitudinal sectional view of an electron gunillustrating the manner in which the various grids forming the electrongun are supported in a conventional manner by a single insulatingsupport member; and

FIG. 3 is a schematic longitudinal sectional view of an electron gun inaccordance with the present invention in which the various grids formingthe electron gun are supported by at least two spaced insulating supportmembers between which are positioned the grid within which theelectrostatic focusing lens is formed.

Referring now to the figures there is illustrated in FIG. 1 the opticalequivalent of a cathode ray tube having a single electron gun thatgenerates a plurality of electron beams that are converged tosubstantially the optical center of a focusing lens. The single electrongun A includes equivalent beam generating sources K K and K which arelocated on a straight line in a plane substantially perpendicular to theaxis of the electron gun and spaced apart from each other by a distanced These beam generating sources K K and K have been converged to an areaof minimum crosssection by means not illustrated such that the area ofminimum cross-section of each of the beams is at the position designatedK K and K The beam generating sources emit three electron beams B B andB respectively, which are refracted by means of a common auxiliary lensL so as to be converged substantially at the optical center sequentlythe beams B and B which diverge from the optical axis and from the beamB lying on such axis are deflected toward the center beam B by means ofconvergence deflectors F and F provided between the electron receivingscreen S and the main lens L and spaced from the latter by a distance 1so that the three beam spots B B and B on the screen are converged orsuperimposed on each other.

With the arrangements shown in FIG. 1 therefor very small beam spots canbe obtained since all three beams B B and B pass through the center ofthe main focusing lens L and thus the focus beams spots are preventedfrom being blurred due to various spherical aberrations. Consequently apicture with a high resolution can be produced. Furthermore, utilizationof the deflectors F and F advantageously facilitates the dynamicconvergence correction with respect to the three beams.

It is to be understood that although FIG. 1 illustrates the beamgenerating sources K K and K as lying in a straight line and theelectron beams being refracted by means of a common auxiliary lens L soas to be converged substantially at the optical center of the mainfocusing lens L the same thing can be accomplished by arranging the beamgenerating sources K K and K on a arcuate surface. In this respect FIG.1 is merely illustrative and not in any way meant to limit the scope ofthis invention.

In FIG. 2 there is illustrated an electron gun A in which the variousgrids forming the electron gun are supported in a conventional manner. Acathode K constitutes the electron beam generating source. The firstcontrol grid G comprises three grid members which are supported in closeopposing relationship to the electron emitting end surface of cathode K.The three grid members have three small apertures arranged on a straightline. The common grid G also has three apertures formed therein inopposing adjacent relationship to the apertures in grid G Arranged inorder following the grid G in the direction away from control grid G aresuccessive open end tubular grids or electrodes G G and G The severalelectrodes 6;, G and G as Well as the grids G G and the cathode K areall assembled together in the illustrated relationship by means of asuitable support 10 of insulating material. The support 10 is positionedadjacent the neck 11 of the cathode ray tube. The electrodes and thegrids are attached to the support 10- by means of clips 12 which areattached to or formed integrally with the support 10. As illustrated inFIG. 2, the various grids and electrodes have essentially the samediameter with the maximum diameter being limited by the inner diameterof the support 10. The focusing lens L is formed in the electrode G Theheight of the focusing lens L is limited by the maximum diameter of theelectrode 6.; which in turn is limited by the inner diameter of thesupport 10.

It is desirable that the reproduced image have as high a resolution aspossible. One of the ways of accomplishing this is to minimize as muchas possible the optical aberrations. Ideally, the focusing lens L shouldhave parallel surfaces in order to eliminate optical aberrations. Thisof course is impossible and it is, therefore, desired that the opposedsurfaces of the focusing lens L have as flat a surface as possible, thatis, a surface having a maximum radius. The radius of the opposedsurfaces of the focusing lens L are, however, limited by the diameter ofthe electrode G The manner in which this is accomplished in the presentinvention is illustrated in FIG. 3. The same parts in FIG. 3 bear thesame reference numerals as in FIG. 2. The major difference between theelectron gun in FIG. 3 and the electron gun in FIG. 2 is that theelectrode G; has been increased in diameter such that it has a diametersubstantially equal to the inner diameter of the neck 11 of the cathoderay tube. This is accomplished by forming the support 10 in two sections13 and 14 with the supports 13 and 14 spaced apart a suificient distanceto allow the electrode 6.; to extend therebetween.

The electrode G is formed with end portions 15 and 16 which fit over theend portions of the grid G and the electrode G The end portions 15 and16 of electrode G are formed with clips or pins 17 for supporting theelectrode G in the supports 13 and 14.

As can be seen from an observation of FIGS. 2 and 3, the embodimentillustrated in FIG. 3 permits the grid 6,; to be made much larger indiameter. This accordingly permits the focusing lens L to also beincreased along its longitudinal axis. This accordingly permits theopposed surfaces of the focusing lens L to have a much greater radiusthan the focusing lens L illustrated in FIG. 2. This results in lessoptical aberrations for the electron beams passing substantially throughthe center of the focusing lens.

In operating the electron gun illustrated in FIGS. 2

and 3, appropriate voltages are applied to the grids G and G and theelectrodes G G and G In this manner an electron lens field isestablished between grid G and the end electrode G which corresponds tothe auxiliary lens L of FIG. 1. In addition, an electron focusing lensfield corresponding to the main focusing lens L of FIG. 1 is formed atthe axial center of electrode 6,, by the electrodes G G and G In orderto cause convergence of the beams B and B which emerge from electrode Galong divergent paths, the electron gun of FIGS. 2 and 3 have deflectingmeans F thus the three beams B B and B emanating from the cathode K aremade to pass through grid G and are modulated with three differentsignals applied between the cathode K and the grid members in grid G Thebeams B B and B pass through the common auxiliary lens L which is formedmainly by the grid G and the electrode G and cross each other atsubstantially the center of the main focusing lens L which isconstituted mainly by the electrodes G G and G Then the beams B B and Bpass through the deflecting means F after leaving the electrode GAccordingly the beams B and B which emerge from the focusing lens Lalong divergent paths are deflected so that three beams B B and B aremade to converge at a point on the electron receiving screen.

It accordingly can be seen that with the present invention the grid G inwhich the focusing lens L is formed can be made much larger in diameterthan with prior art electron guns. This permits the focusing lens L tobe increased in height which accordingly permits the opposed surfaces tohave a much larger radius. In this manner the amount of opticalaberrations is substantially reduced.

In the foregoing description the electron gun embodying this inventionhas been described as being applied specifically to colored picturetubes in which a single gun is employed to produce three electron beamswhich are intensity modulated with the usual red, green, and blue colorsignals. However, it is obvious that an electron gun in accordance withthis invention can be used in any other cathode ray tube requiring aplurality of beams which are to be focused at a common spot or atseparated spots on an electron receiving screen.

Although illustrative embodiments of electron guns according to thisinvention have been described in detail herein with reference to theaccompanying drawings, it is to be understood that the invention is notlimited to those precise embodiments and that various changes andmodifications may be made therein by one skilled in the art withoutdeparting from the scope or spirit of the invention as defined in theappended claims.

What is claimed is:

1. A cathode ray tube having a face plate with an electron receivingscreen thereon and a neck portion opening in the direction toward saidscreen, an electron gun disposed within said neck portion and comprisingbeam generating means for producing a plurality of electron beamsoriginating in a plane including the longitudinal axis of the tube andfocusing lens means for focusing said beams on said screen, saidfocusing lens means including first, second and third tubular electrodesarranged axially with said first and third electrodes spaced from eachother and said second electrode interposed between said first and thirdelectrodes and having at least a central portion that fits closelywithin said neck portion and has a diameter substantially greater thanthat of said first and third electrodes, and mounting means for locatingsaid gun within said neck portion of the tube, said mounting meanscomprising axially spaced first and second sets of longitudinal supportbars arranged around said first and third elec trodes, respectively, andfitting within said neck portion, said central portion of the secondelectrode projecting radially between the adjacent end portions of thebars of said first and second sets, support members projecting radiallyfrom said first and third electrodes and secured to said support bars ofsaid first and second sets of support bars for mounting said first andthird electrodes therefrom, and additional support members extendingfrom said second electrode and secured to said adjacent end portions ofthe support bars for mounting said second electrode therefrom.

2. A cathode ray tube according to claim 1, in which said secondelectrode has end portions of reduced diameter, and said additionalsupport members extend radially from said end portions of the secondelectrode to said adjacent end portions of the support bars.

3. A cathode ray tube according to claim 1, in which said plurality ofelectron beams intersect each other substantially at the optical centerof the lens defined by said focusing lens means.

References Cited UNITED STATES PATENTS 2,792,515 5/1957 Broderick et a1.313-82 2,859,378 11/1958 Gundert et a1. 2,945,143 7/1960 Shapiro 313823,258,627 6/1966 Paull 31382 ROBERT SEGAL, Primary Examiner US. Cl. X.R.313251

